Method of eliminating offset



Patented Jan. 11, 1949 UNITED STATES PATENT OFFICE METHOD OF ELIMINATINGOFFSET Charles B. Cotherman, Goshen, Ind.

No Drawing. Application October 1, 1945, Serial No. 619,701

4 Claims. 1

1n the art of printing, one troublesome factor is the tendency of staticelectricity to interfere with the proper positioning of a sheet of paperon the platen of a printing press, which carries the sheet into printingcontact with the type, plate, or printin cylinder. Similarly, staticelectricity is responsible for considerable difilculty in speedilyremoving the sheet after it is printed. It also interferes with thejogging of the removed sheets, that is to say, the evening-up of a stackof the printed sheets.

The objects of the present invention are to provide a method ofeliminating the adverse efiects usually attributed to static electricityin the art of printing and more specifically, to facilitate thepositioning and removal of work on and from the platen of a printingpress, to eliminate offsetting, and to facilitate jogging of the printedwork.

The platen of a printing press is usually built up with the so-calledmake ready and covered with a top sheet which is usually referred to asthe draw sheet.

According to the present invention, the surface of the draw sheet hasapplied to it a thin coating of a composition consistin of oil andpowdered soapstone. High quality lubricating oil of the grade known asNo. (SAE rating) is employed together with the best grade of very finelypowdered soapstone (commercially available as No. 1 powdered soapstone),These ingredients are thoroughly mixed in proportions which may varyfrom about one-half pound to 2 pounds of powdered soapstone to one quartof 011.

For application in the printing art, as already explained, theproportions of about one pound of soapstone to one quart of 011 givesexcellent results. Such a mixture is a very thick or viscous mixture,but it has the capacity of being spread into a very thin film so that avery small quantity of the composition is required for covering theentire area of the draw sheet on an average size printing press.

The thin coating of the composition may be wiped over the draw sheet andevenly spread and it will so effectively adhere to the draw sheet thatnone of it will leave the draw sheet and adhere to the paper placedthereon for printin purposes, or, at least if any of the compositiondoes adhere to the printing paper, it is unnoticeable and hence isnegligible.

When the draw sheet of a printing press is coated with the describedcomposition, it is found that the sheets to be printed upon have notendency to adhere to the draw sheet and that they can be quickly slidacross the surface of the draw sheet into their proper position forprinting, and then easily withdrawn when the printing is completed. Itis sometimes advantageous to adjust the usual sheet gripping means tohold the sheets somewhat more tightly during the travel of the platencarrying the sheet into printing engagement with the type since theelimination of sheet adherence to the draw sheet sometimes results in atendency for the sheet to be thrown out of place as an incident to itsmovement with the platen.

In addition to facilitating the insertion and removal of printin sheetsfrom the press, the elimination of static electricity from the printedsheets eliminates ofisetting which results from a pronounced tendencybelieved to be due to static electricity, for the printed sheets, whenpiled, too tightly adhere to one another. When the described compound isemployed in the manner explained, the printed sheets will form arelatively loose stack so that the ink will set sufiiciently to preventoffset before the printed sheets settle into a tighter stack. Thiselimination of huddle (sheet to sheet adhesion) also facilitatessubsequent jogging, that is to say, evening-up of the stack of sheets,which have been printed and more or less haphazardly assembled in thestack.

Another important benefit of the use of the composition in the printingart as explained, is that the composition protects the draw sheetagainst excessive wear so that it remains good for use for a much longerperiod than under ordinary conditions. In ordinary practice, therepeated application and withdrawal of work from the draw sheet coveredsurface of the platen, appears to be accompanied by a tendency of eachprinted sheet to remove with it, a certain amount of lint-like fiberfrom the surface of the draw sheet. This tends to produce a nap-likesurface on the draw sheet, which in a short time becomes unfit forfurther use.

When a draw sheet is coated with the described composition, the tendencyof the printed sheets to pick up fibers from the draw sheet appears tobe wholly eliminated, and the surface of the draw sheet retains itsnormal smoothness and hardness for a much longer period than does anuntreated sheet.

The mixture described should be thoroughly stirred before it is usedbecause the soapstone ingredient tends to settle out of the oil. Theoil, which constitutes a carrier for the soapstone, appears to serve thepurpose of adhesively anchoring the soapstone particles to the drawsheet.

The carrier facilitates spreading of the soapstone into a thin andalmost imperceptible coat on the surface of the draw sheet. However, theoil may also otherwise contribute to the operativeness of the describedmethod and mixture because of its lubricating properties.

I claim:

1. The method of facilitatin Printing press work positioning and removalwhich consists in applying to the draw sheet of a printing press platen,a mixture of oil and finely powdered soapstone.

2. The method of facilitating printing press work positioning" andremoval which consists in applying" to the draw sheet of sprinting pressplaten, a mixture of oil and. finely powdered Soapstone, the mixturebeing in the proportions of from one-half pound to two pounds ofsoapstone, to about one quart of oil.

3. The method of facilitating printing press work positioning andremoval which consists in applying to the draw sheet of a printing pressplaten, a surface coating of finely powdered soap-,

stone mixed with oil.

4. The method of eliminating the efiects of static electricity onprinted work which consists in applying to the draw sheet of theprinting press platen on which the work is printed, a mixture oflubricating oil and powdered soapstone.

CHARLES B. COTHERMAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

' UNITED STATES PATENTS Number Name Date 110,032 Gorman Dec. 13, 1870142,930 Muller Sept. 16, 1873 982,726 i Johnson Jan. 24, 1911 1,566,800MacAurthur Dec. 22, 1925

